Prior to the present invention a variety of thermoplastic and thermosetting polymeric materials were commercially available for use in orthopedic applications. For example, a number of polymeric materials which exhibit thermoplastic properties are known to be useful for the immobilization of fractures. Such materials include, for example, those described in U.S. Pat. No. 2,385,879 which are indicated to be comprised of a copolymer of vinyl acetate and organic phosphate ester plasticizers. Also in U.S. Pat. No. 3,692,023 there is disclosed the use of a poly-caprolactone as a cast material employing porous webs impregnated with the polymer.
Thermoplastic compositions comprised of poly(epsilon-caprolactone), cis-1,4-polyisoprene, and optionally, an ionomer which is a copolymer of ethylene and acrylic or methacrylic acid have been disclosed and claimed in U.S. Pat. No. 4,274,983. Other thermoplastic polyester resins such as those disclosed in U.S. Pat. No. 4,404,333 are indicated to be useful in orthopedic cast material. This patent discloses and claims thermoplastic resins comprised of the reaction product of linear polyester resins and epsilon-caprolactone.
Other orthopedic devices, methods of preparation and use wherein poly(epsilon-caprolactone) is employed as the thermoplastic material are disclosed in the patent literature. For example, in U.S. Pat. No. 4,175,177 there is disclosed crosslinkable copolymers of a lactone, such as epsilon-caprolactone and poly-functional acrylates. It is indicated in the patent that the crosslinked copolymers can be used as plasticizers for vinyl resin compositions or as materials of construction for orthopedic casts and splints. Orthopedic devices are also disclosed in U.S. Pat. No. 4,226,230 which is directed to a method of applying an orthopedic cast which is comprised of a flexible bandage material in the form of a netting and which has been coated with a crosslinkable copolymer of a lactone and an acrylate monomer.
In U.S. Pat. No. 4,238,522 there is disclosed a method for producing a bandage material which can be convertible to an orthopedic cast by first applying an electrically conductive coating to the strands of a netting material and thereafter electrostatically spray coating the strands with a crosslinkable copolymer powder comprised of a lactone and a polyfunctional acrylate monomer. The bandage material is heated to a temperature at which the crosslinked copolymer is soft and self-adherent and is then wrapped around the body portion in overlaying layers to conform to the body contours and then cooled to a rigid state.
An orthopedic cast made from a thermoplastic polyester such as poly(epsilon-caprolactone) which has been subjected to electron radiation is disclosed in U.S. Pat. No. 4,240,415. It is indicated in the patent that the radiation effects crosslinking and desirable modification in the modulus of elasticity. In U.S. Pat. No. 4,286,586 which is a divisional of the above-mentioned U.S. Pat. No. 4,226,230 the invention disclosed and claimed therein is directed to orthopedic casts comprised of a crosslinkable copolymer prepared from a lactone and a polyfunctional acrylate monomer.
A process for producing orthopedic structures is disclosed in U.S. Pat. No. 4,316,457 wherein a bandage material is impregnated or coated with a solvent solution of a polyurethane prepolymer, a bifunctional chain extender and a catalyst. A bifunctional oligomer which can be reacted with diisocyanates for the preparation of polyurethane prepolymers are oligomers of cyclic lactones such as epsilon-caprolactone.
A cold water curable orthopedic cast is described in U.S. Pat. No. 4,427,002. The cast is comprised of a bandage material coated with a cold water curable polyurethane prepolymer. In U.S. Pat. No. 4,483,333 an orthopedic cast material is prepared from a mixture of polyethylene and a thermoplastic polyester having a melting point between 50.degree. C. and 100.degree. C. and a molecular weight of over 5000. Poly(epsilon-caprolactone) and polyethylene are disclosed as the preferred components of the cast system.
Other materials are currently available for use in orthopedic casts and have met with some degree of success as commercially acceptable products. Products containing poly(epsilon-caprolactone) have proven to have significant potential as useful cast materials. Many such products have filler and impact modifiers added to improve basic characteristics and provide a non-tacky product. However, for certain applications, improved elasticity during forming, improved resistance to fingerprinting and improved toughness are desired. For such applications crystalline poly(1,4-isoprene) is widely used although it is characterized by very poor self adhesion. Hence, it was desirable to develop an orthopedic cast material which would inherently possess all of the desired properties and exhibit excellent elasticity, does not easily fingerprint, retains adhesion and has high toughness and flexural strength.
Accordingly, the present invention provides an effective method by which poly(epsilon-caprolactone) can be transformed into a material useful for certain orthopedic applications whereby improved toughness, improved resistance to fingerprinting, and greatly improved elasticity during molding are present. This material also retains excellent self-adhesion whih the polyisoprene products of the prior art do not possess. The combination of properties can only be achieved by a blend of poly(epsilon-caprolactone) and a specific thermoplastic polyurethane is hereinafter described. Other aliphatic polyesters having crystalline melting points of 50.degree.-70.degree. C. may be substituted for the poly(epsilon-caprolactone) in the above blends.